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Subject[tip:x86/timers] sched/clock: Use static key for sched_clock_running
Commit-ID:  46457ea464f5341d1f9dad8dd213805d45f7f117
Gitweb: https://git.kernel.org/tip/46457ea464f5341d1f9dad8dd213805d45f7f117
Author: Pavel Tatashin <pasha.tatashin@oracle.com>
AuthorDate: Thu, 19 Jul 2018 16:55:43 -0400
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 20 Jul 2018 00:02:43 +0200

sched/clock: Use static key for sched_clock_running

sched_clock_running may be read every time sched_clock_cpu() is called.
Yet, this variable is updated only twice during boot, and never changes
again, therefore it is better to make it a static key.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-25-pasha.tatashin@oracle.com

---
kernel/sched/clock.c | 16 ++++++++--------
kernel/sched/debug.c | 2 --
2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 422cd63f8f17..c5c47ad3f386 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -67,7 +67,7 @@ unsigned long long __weak sched_clock(void)
}
EXPORT_SYMBOL_GPL(sched_clock);

-__read_mostly int sched_clock_running;
+static DEFINE_STATIC_KEY_FALSE(sched_clock_running);

#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
/*
@@ -191,7 +191,7 @@ void clear_sched_clock_stable(void)

smp_mb(); /* matches sched_clock_init_late() */

- if (sched_clock_running == 2)
+ if (static_key_count(&sched_clock_running.key) == 2)
__clear_sched_clock_stable();
}

@@ -215,7 +215,7 @@ void __init sched_clock_init(void)
__sched_clock_gtod_offset();
local_irq_restore(flags);

- sched_clock_running = 1;
+ static_branch_inc(&sched_clock_running);

/* Now that sched_clock_running is set adjust scd */
local_irq_save(flags);
@@ -228,7 +228,7 @@ void __init sched_clock_init(void)
*/
static int __init sched_clock_init_late(void)
{
- sched_clock_running = 2;
+ static_branch_inc(&sched_clock_running);
/*
* Ensure that it is impossible to not do a static_key update.
*
@@ -373,7 +373,7 @@ u64 sched_clock_cpu(int cpu)
if (sched_clock_stable())
return sched_clock() + __sched_clock_offset;

- if (unlikely(!sched_clock_running))
+ if (!static_branch_unlikely(&sched_clock_running))
return sched_clock();

preempt_disable_notrace();
@@ -396,7 +396,7 @@ void sched_clock_tick(void)
if (sched_clock_stable())
return;

- if (unlikely(!sched_clock_running))
+ if (!static_branch_unlikely(&sched_clock_running))
return;

lockdep_assert_irqs_disabled();
@@ -455,13 +455,13 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

void __init sched_clock_init(void)
{
- sched_clock_running = 1;
+ static_branch_inc(&sched_clock_running);
generic_sched_clock_init();
}

u64 sched_clock_cpu(int cpu)
{
- if (unlikely(!sched_clock_running))
+ if (!static_branch_unlikely(&sched_clock_running))
return 0;

return sched_clock();
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index e593b4118578..b0212f489a33 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -623,8 +623,6 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
#undef PU
}

-extern __read_mostly int sched_clock_running;
-
static void print_cpu(struct seq_file *m, int cpu)
{
struct rq *rq = cpu_rq(cpu);
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